MTFCA Forum

Is it necessary to keep the heater connected to the carb while driving in warmer temps. I may take my T out for a short trip to the mailbox in winter, but that is not often. I suppose in doing so even a short drive might freeze up the carb. Thank you to any responders!

No. "Carb ice forms because the pressure drop in the venturi causes the air to "cool," and draw heat away from the surrounding metal of the carburetor venturi. Ice then can begin collecting on the cooled carburetor throat. This is the same principle that makes your refrigerator or air conditioner work." It has to be cool and moist enough to ice the carb and heat pipe.

One thing I'll disagree with Rich on is that you in no way need for it to be cool. My worst frosting over of a carb (with horrible running results) was on my '13 with an original aluminum intake manifold at 92F and 90%+ humidity.

As a new owner of Model T's I found it astounding that I needed a hot air pipe in the middle of blazing summer in Florida. Over the years I've found that not all cars need hot air pipes and 2 of my 4 cars NEVER needed one at any time. The '13 sure did, though, and the hot air pipe transformed its performance from a dog which needed super-rich carb setting to run (until it fouled the plugs in 3 miles) to a car which now runs far leaner and I haven't pulled the plugs for a cleaning in probably 7-8 years.

So, in my experience, hot or cold has less influence in needing one than humidity does.

Now that I'm in WY, they do not seem to be needed under any circumstance (so long as I can still crank 'em up)

I drove my car a little bit the first winter with no heat stove with no problems, or so I thought. Once it got warm out ( and we have no humidity here in the summer) I found the intake very cold and soaked in condensation even after long drives on days that were very hot. I suppose the motor, once warmed up, makes more vacuum over even short trips than it does during the limited, cold weather jaunts around the industrial park I had done up to that point. Admittedly I put on the chromed one as extra bling to go with the theme, but on the first day crossing the valley I got way smoother throttle response, a little more power and it was easier restarting the already hot engine. From what I have seen most do not use them around here, but my experience with others is limited. I would leave one in place on a normally configured intake system even somewhere tropical from now on. Obviously just my opinion based on limited experience, and of course, results will vary. Chris, in Boulder

What Scott says is what it is all about. Here in Alabama they are needed when it is 100 deg and high humidity. Which is all summer. It is all about carb icing not gas vaporizing. Dan

It's about water condensation, icing and fuel vaporization.

Icing cannot occur if the air is very dry, but the carburetor and manifold will get very cold and impede vaporization of the gasoline until the engine gets warm enough to circulate water and add some heat to the intake air. You don't need manfold heat in warm, very dry weather, but in cold weather or humid weather, or cold, wet, humid weather, you do need one. They're easy to install and remove, so there's no need to avoid using one. Alcohol blended gasoline seems to do little to prevent condensation/freezup.
A carburetor acts just like an expansion valve in a refrigeration unit, especially at light throttle.

The problem with this item is it makes it really hard to install a air cleaner which I want!

Funny you mention the air filter! I drove the $#!* out of the no hood, no fenders roadster around the very dusty, gravelly industrial park like a rally car when testing it for traffic worthiness. I figured an air cleaner would be prudent and tried to send it up by the exhaust (yup, with bathroom plumbing, haha) to at least get fairly hot air. I briefly considered a screen or some chore boy in the new heat stove but would hate to have any material sucked in! The hot air pipe is pretty far up and away from the road but on a really fresh engine build I think I’d try to figure out a combo. New everything deserves a dirt free mixture for sure. Mine is ummm, “experimental”…. Really any air down by the exhaust is pretty hot, but I noticed a big difference with my engine that is “medium” fresh, and our local weather, which is different every few minutes….-Chris, in Boulder

I can't run without an air filter, so I do without a heat heat pipe. It's usually hot or dry here, so I don't have a lot of problems, but the car does run better the first few miles on very dry days, even in cool weather. I don't drive in extreme cold. I'd like to have a Donaldson-type air filter mounted on the radiator stay rod with some kind of heat pipe arrangement with a dash control. Besides quicker warm up and freedom from carburetor icing, the stock Ford heat pipe arrangement helps to shield the fuel bowl on the cowl tank cars from manifold heat, which can be an issue in very hot weather.

TXGOAT2 wrote: ↑

Mon Jan 16, 2023 2:32 pm

. …Alcohol blended gasoline seems to do little to prevent condensation/freezup. …

In addition to the venturi effect, vaporization of the fuel also absorbs a lot of heat. I don’t know for sure, but I would think alcohol would exacerbate the problem.

I'm thinking that if there was even a tiny chance that a Model T would run OK without the heat tube, Henry would not have installed one. In all my years (65) , of playing with old and new cars, I can't recall any car engine not having some sort of device or mechanism to provide heat to the intake manifold. T's are very forgiving and yes, they'll run without one but it's been my experience that they run better with the heat tube.......better fuel atomization, no more intake icing, better fuel economy, and probably a lot less carbon build-up in the head and on the spark plugs. As well, unless your engine has a high flow carburetor, bigger valves and maybe a higher lift cam, the "performance" will not be compromised by the heat tube.

I live in Wisconsin, the only time I ever had a Carburetor frost was in July. It was hot and humid. I have 5 Model T’s and I have the manifold tubes on them all. They run ok in the winter also.

Alcohol and gasoline both refrigerate when they evaporate. So does any volatile fluid, including water. "Swamp coolers" evaporate water at a rapid rate to cool the air passing through them. They work very well in hot, dry climates. Alcohol in gasoline has an anti-freeze effect, but it soes not seem to be sufficient to offset the carburetor freeze up problem.
Back when I washed parts in leaded gasoline, I very nearly froze my hands doing it in cold weather. In warm, humid weather, gasoline in an open container will cool off enough to draw moisture out of the air.
Highly volatile liquids, like propane, either, etc, "Freon", have a very intense refrigerating effect due to their very rapid evaporation rate at normal atmospheric pressure.

If you are just driving along on a tour with a good running T engine and the engine backfires and stops for no known reason, look at your carburetor.

If there is ice in the center area and that air inlet pipe is missing, your problem is the frost in the carb thinned your air/gas mixture to an extreme too thin to operate level.

I owned my first T for ten years before I learned how important that air inlet pipe was and why it was needed.

My real confusion was, if I let the engine sit for about 15 to 20 minutes, it would start right up and run good again for a while.

Sometimes, especially if the temperature had raised and the morning fog had cleared up, it would run good for the rest of the day.

The downside to the heat pipe is loss of power. Some few years ago someone did a dynamometer test, reported on in the then Forum, on T engines with and without heat pipes and found a 10% loss of power using the heat pipe. When I lived in Ohio I always used a heat pipe, even on the odd day year-round when it didn't snow. Now in Western North Carolina I have't used one in a long time, but may put one back on after reading the threads above. Since I drive brass era T's I have 22 hp to begin, so will only drop back to what the later T's gave for hp.

Stopping the engine stops the refrigeration process and allows the carburetor and manifold to warm up rapidly. After a few minutes, the engine should start and run normally, and will probably continue to run normally under most conditions, since hot air from the radiator usually prevents further icing or condensation issues as long as the car warmed up is running. Under conditions highly conducive to icing, such as very high humidity, cool humid weather, and running the engine at light throttle or idle, the icing problem may continue unless a heat pipe is installed. The heat pipe can cause some loss of power in hot weather. In such cases, and under most conditions, it can be removed with no ill effect. Ideally, the heat pipe would have a dash mounted control to allow using it only when needed, and to the degree needed.

I have a 1914 Touring and I ran it for a season without the carb heater. The car started and ran well in the summer heat without the carb heater, but I started driving it to work and later in the year it started getting cool in the morning and it did not run as well. I put the carb heater on and immediately noticed how much quicker the engine smoothed out and how much leaner I could run it. If I have any problems in the heat of the summer I may try taking it off, but anytime the air is cool and/or damp I plan to run with it on.

bdtutton wrote: ↑

Wed Jan 18, 2023 2:40 pm

I have a 1914 Touring and I ran it for a season without the carb heater. The car started and ran well in the summer heat without the carb heater, but I started driving it to work and later in the year it started getting cool in the morning and it did not run as well. I put the carb heater on and immediately noticed how much quicker the engine smoothed out and how much leaner I could run it. If I have any problems in the heat of the summer I may try taking it off, but anytime the air is cool and/or damp I plan to run with it on.

I have a 14 also & had the same experience. As a compromise, I drilled 4-1/2" holes in the lower back side.
Might have got a little more performance, but still get enough heat.

Would the installation of high compression pistons or head increase or decrease the possibility of carb icing in your opinion?

browning wrote: ↑

Thu Jan 19, 2023 11:55 am

Would the installation of high compression pistons or head increase or decrease the possibility of carb icing in your opinion?

Increase. There is a larger volume of mixture moving faster. More suck & more blow.

I live in Florida, where it is almost always warm and I have tried it both ways, with and without the hot air pipe and my 1926 coupe has always run better with the hot air pipe installed. I have also tried every type of timer there is and have circled around back to using the original roller type timer I started with. I have decided that it is a waste of my time to try and challenge Ford’s engineers and designers, so except for my Guinn wooden band liners and my high capacity outside oil line, my engine is basically the way it came off the assembly line in 1926. Jim Patrick

The icing issue occurs primarily at idle and light throttle before the engine warms up. Going downhill with the throttle closed in cool wet weather could cause temporary icing.

The solution in all cases is preheating the intake air, whether by use of some apparatus like the heat pipe or a water jacketed intake manifold, or by raising the underhood temperature by means of a winterfront or some other means. Normal engine operation will get the underhood temperature high enough to prevent icing issues under most conditions once the engine warms up. Icing is very rarely a problem when the engine is warmed up and running with some load and the throttle off idle most of the time.

The original Ford equipment is almost certainly the most effective and practical solution to the icing problem for most conditions. The Ford system, modified with some type of shutter/diversion device, would be an improvement. Ideally, you'd have a mmanual or thermostatic intake air preheating device and a hot spot manifold with a manual or thermostatic control.

speedytinc wrote: ↑

Thu Jan 19, 2023 12:01 pm

browning wrote: ↑

Thu Jan 19, 2023 11:55 am

Would the installation of high compression pistons or head increase or decrease the possibility of carb icing in your opinion?

Increase. There is a larger volume of mixture moving faster. More suck & more blow.

Really? Have those things increased the displacement of the engine?

Txgoat2 nailed it….
Aircraft have an exhaust heated CARB HEAT box. Normal aircraft operation is carb heat OFF. When icing is detected, pulling “carb heat” directs heated air into the carb to remedy or prevent carb ice. Heated intake air is an ABSOLUTE reduction of power. Carb icing is readily apparent in a slow and continued loss of RPM’s. In high probability carb icing conditions, I will regularly pull carb heat for a few seconds to eliminate the start of icing. After icing is already in process pulling carb heat melts the “chunk” of ice and the engine swallows a drink of water…with attendant engine sputter….and attendant sphincter sputter. A “Y” pipe with air cleaner/cold air and heat pipe hot air would be a very simple arrangement to make. Then diverter is a box with 2-position flapper.

Typical aircraft carb-heat box. In my mind, this would LOOK very period correct on a T.

The Stromberg OF SET UP has a press steel unit that wraps around a portion of the stock intake manifold, in addition a steel flex tube attached to the exhaust manifold via a piece that is tapped into the EM somewhere between the 1 & 2 cylinder. That tube then runs into and then a separate flex tube coming out of the stamped piece on the intake to preheat/vaporize the fuel before it enters the combustion chamber. I always thought that was a much better way plus you could put a filter on the carb if you’d like. The problem is those pieces are hard to find. I don’t think it would be difficult to mimic that system though. Dan McEachern has a wilmco combination exhaust for sale on the classifieds that appears to have had that setup attached at one time. In theory I suppose the radiant heat from the pressed steel piece would also warm the carburetor a bit. I’d post a picture of the exhaust Dan has but don’t have his permission to. You can go to the classifieds though and see his post.

Thanks for posting the Stromberg set-up John. Actually, the Stromberg OF and RF along with the Rayfield UF, the Wheeler-Schebler FAX8 and FA2, and the U&J carburetors designed for the "T" all were sold with a provision for manifold heat and detailed instructions as to how to install it. Along with this, every Model T Ford sold new (after 1910) came with a heat pipe, and now we're questioning if it's really necessary. What am I missing??

Bruce if those guys knew what they were doing back in the day you’d probably see those vehicles still around. Your not missing a thing

Modern carbureted vehicles with missing or inoperative intake heat devices will suffer from condensation/freezeup issues under some conditions. Inline 4 and 6 cylinder engines are more prone to it. I believe that some fuel injection systems have some provision for heating the throttle body. They are less prone to the problems, but frost can occur around the throttle plate at idle under some conditions.